Preheat oven to 400 degrees. In a medium skillet, over medium heat, saute onion in oil until tender. Stir in salsa and spinach, cooking for 2 minutes more. Transfer to a 1 1/2 -quart baking dish. Stir in 2 cups Monterey Jack cheese, the cream cheese, cream and olives. Sprinkle with pecans. Bake for about 30 minutes or until hot and bubbly (covered with foil during the last 15 minutes to prevent burning). Top with remaining Monterey Jack cheese. Serve hot.